Almost everyone I know, whether a psychologist or not (and I do have one or two friends who aren't!) is fascinated by sleep. Be it dreaming, sleep-walking (or other forms of parasomnia) or just comparing how much they think they need each night, it's a frequent source of amusement and debate. How strange, then, to think that despite decades of research, we still know relatively little about the function of sleep, or even what 'normal' sleep looks like. Compare what you know about sleep to what you know about diet (arguably something of comparable importance to our health) for example. Many people now analyze their diets in great detail, but do we have any idea how we might do have same for our sleep?

One recent attempt to help rectify this, published in the journal PLOS One by Kevin Peters and his team, examined if age plays a role in what normal sleep looks like and the phases that make it up (termed 'sleep architecture), looking for similarities and differences between the sleep patterns of young and older adults.

Stages of sleep, including REM and sleep spindles

We already know that as people age, they tend to sleep less efficiently (sleeping for less time and spending more time awake in the night) and spend less time in REM sleep (rapid eye movement sleep, a stage of sleep where eyes move rapidly in different directions). Aging is, of course, associated with a general cognitive decline in many areas. Whether sleep changes could be a cause or an effect of these changes, however, is not yet known. We also do not yet know whether changes to certain aspects of sleep might be more important than others in accelerating or preventing cognitive decline.

Peters et al looked at two particular aspects of sleep in groups of 24 young and old adults (mean ages 20.75 and 71.17 respectively), REMs and sleep spindles (bursts of brain activity that occur in phase two of sleep, usually immediately after an outbreak of muscle twitching). Both of these have been separately linked to cognitive function in previous studies, but none of these studies have looked at the relationship between the two across different age groups. To try to make the sleep as 'natural' as possible, Peters et al excluded people with signs of depression or sleep disorders (both of which can lead to abnormal sleep patterns) and all participants had an 'acclimatization night' sleeping in their normal beds with the measurement electrodes attached but not recording.

Having said how poorly understood sleep is, it is perhaps not surprising that the results turned out to be quite complicated! Young adults had greater spindle density than older adults, but the two age groups did not seem to vary significantly in the density of their REM. Perhaps this shows that age affects sleep spindles more than REM, but this contrasts with the findings of some other studies so need to be examined in more detail. In addition, another important finding was the huge amount of variability between individuals' sleep patterns. There seem to be large individual differences between the way we all sleep and Peters et al found that in some areas (such as wakefulness in the night) these differences may actually increase as we age.

What conclusions can we draw then, from this contribution to the study of such a familiar yet mystifying topic? Given that sleep is so crucial to all of us, I find it amazing to think that it can vary so much from person to person. Finding areas of sleep that may be more important than others (for example, a very early possible link here between sleep spindles and ageing) may be exciting, but given all this variability, generalizing any findings from future experiments to all of us will surely prove a huge challenge. The baffling and intriguing study of sleep seems set to continue to give us sleepless nights for a good while yet.